Efficient synthesis of bottle-brush polymers enabled by selective photoactivation strategy in NIR-induced PET-RAFT polymerization

Bottle-brush polymers possessing densely grafted side chains have special properties that are distinct from linear macromolecules. Herein, an efficient method for preparing bottle-brush polymers based on a selective photoactivation strategy in the photoinduced electron/energy transfer reversible addition-fragmentation chain transfer (PET-RAFT) polymerization was developed. A methacrylate monomer 2-(2-(dodecylthiocarbonothioylthio)propionate)ethyl methacrylate (DTPEMA) containing a 2-(dodecylthiocarbonothioylthio)propionate (DTP) unit with a secondary R group was designed. Utilizing the unique selectivity of metal naphthalocyanine photocatalyst zinc 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (ZnTtBNc) toward trithiocarbonate with tertiary R group, the PET-RAFT polymerization of DTPEMA catalyzed by ZnTtBNc was performed under near infrared (NIR) light (λ_max = 760 nm) irradiation at room temperature, using 4-cyano-4-[(dodecylsulfanylthiocarbonyl)-sulfanyl] pentanoic acid (CDTPA) with a tertiary R group as a chain transfer agent (CTA). Proton nuclear magnetic resonance (¹H NMR) and gel permeation chromatography (GPC) results demonstrated that the DTP units in the side chains were inert during the polymerization. By grafting poly(methyl acrylate) (PMA) from PDTPEMA via thermal-initiated RAFT polymerization, well-defined P(DTPEMA-g-PMA) bottle-brush polymers could be afforded. Furthermore, the film prepared from the bottle-brush polymer exhibited excellent scratch self-healing property due to the interlocking of side chains.